Radio frequency switches are basic building blocks for communication and control systems and are used for multiplexing of signals to achieve system reconfigureability and dynamic control. Radio frequency switches may be used in such applications as portable/mobile/satellite communication systems (e.g. cell-phones, PDAs, laptops, phased array antennas, sensors, transceivers etc.). As communication systems approach higher data rate (Giga Bytes per second) and multi-functional operation, stringent requirements are placed on radio frequency switches. Some of these requirements include low power consumption, high reliability, high switching speed, high isolation, low insertion losses, ease of integration/implementation, as well as affordability. In particular, for 3 G (third generation) wireless phones and space-based applications, low power consumption is critical to ensure reliable, long lifetime operation on limited power supplies. MEMS or solid-state based switches which are currently used are incapable of meeting future demands due to associated disadvantages. MEMS devices utilize complicated manufacturing processes and are expensive to make. See FIG. 8, FIG. 8 is a table comparing electronic, physical and cost properties of MEMS, Solid State, and Nanoionics switches.
The present state-of-the-art radio frequency devices employ electronic, mechanical, or a combination of the two (electromechanical) processes to induce a change in state (on/off). Radio frequency switching applications usually employ solid state switches (i.e., diodes, FETs) or microelectromechanical systems (MEMS), both of which possess associated weaknesses. Solid state diodes can be produced cost-effectively to operate at low voltages (1-3V) and high speeds (ns), but suffer from higher insertion loss, high DC power consumption, low isolation, and the generation of third-order harmonics/intermodulation distortion (IMD). MEMS-based switches provide low insertion loss (˜0.2 dB), low DC power consumption (˜pW), high isolation (>30 dB), and good IMD performance, but exhibit reliability problems (e.g., stiction, moving parts), slower switching speeds (ps), high actuation voltages (5-50V) which require complex circuitry, and relatively complicated processing steps. Furthermore, MEMS packaging presents additional problems which need to be addressed before widespread use is realizable.
Chalcogenide glasses contain a large number of group VI or “chalcogen” atoms (S, Se, Te and O) and have a wide range of physical characteristics. Stable binary glasses typically involve a group IV or group V atom, such as Ge—Se or As—S. Non-oxide glasses usually are more rigid than organic polymers but more flexible than a typical oxide glass. The flexibility of these materials offers the possibility of the formation of voids through which the ions can readily move from one equilibrium position to another. The addition of Ag or Cu (Group I elements) transforms the chalcogenide glass into an electrolyte as these metals form mobile ions within the material. The ions are associated with the chalcogen atoms. The high dielectric constant of the glass materials (typically around 10), reduces the coulombic attractive forces between the charged species and allows high ionic mobility. The conductivity of the ternary glasses is a strong function of the mobile ion concentration. “Ternary” generally means a compound having three elements.
“The transformation that occurs in ternary electrolytes at over a few atomic percent of metal is not a subtle one by any means. Indeed, the material undergoes considerable changes in its nanostructure that have a profound effect on its macroscopic characteristics. These changes are a result of phase separation caused by the reaction of silver with the available chalcogen in the host to form distinct regions of Ag2Se in Ag—Ge—Se and Ag2S in Ag—Ge—S ternaries.” See, Devices based on mass transport in solid electrolytes, Michael N. Kozicki and Maria Mitkova, Center for Applied Nanoionics, Arizona State University.
“The addition of Ag (or Cu) to the chalcogenide base glass can be achieved by diffusing the mobile metal from a thin surface film via photo dissolution. The process utilizes light energy greater than the optical gap of the chalcogenide glass to create charged defects near the interface between the reacted and unreacted chalcogenide layers. The holes created are trapped by the metal while the electrons move into the chalcogenide film. The electric field formed by the negatively charged chalcogen atoms and positively charged metal ions is sufficient to allow the ions to overcome the energy barrier at the interface and so the metal moves into the chalcogenide. Prior to the introduction of the metal, the glass consists of GeS4 (GeSe4) tetrahedra and, in the case of chalcogen-rich material, S (Se) chains. The introduced metal will readily react with the chain chalcogen and some of the tetrahedral material to form the ternary. This Ag chalcogen reaction, which essentially nucleates on the chalcogen-rich regions within the base glass, results in the nanoscale phase-separated ternary.” See, Devices based on mass transport in solid electrolytes, Michael N. Kozicki and Maria Mitkova, Center for Applied Nanoionics, Arizona State University.
Nanoionics concerns itself with materials and devices that rely on ion transport and chemical change at the nanoscale. The chemical change takes the form of an oxidation/reduction reaction of ionic metal species within some base material to essentially “grow” metal on the surface (or within a film) at low energies.